The present invention relates to a method and apparatus for reducing the temperature of an optical fiber. In particular, the present invention relates to an optical fiber cooling apparatus comprising a plurality of separate inner cooling chambers through which a plurality of refrigerant tubes extend to form an enlarged heat exchange surface.
When drawing an optical fiber at high speed, rapid cooling of the optical fiber is important to achieve a good coating application on the fiber and good optical equality of the fiber. In particular, if the temperature of the optical fiber is elevated during the coating application, the coating diameter decreases, control of the coated fiber diameter decreases, and instability of the coating application increases (e.g., loss of coating, lumps, neck-downs, etc.). Further, a high draw speed of the optical fiber is necessary to increase productivity and decrease production cost.
In order to produce an optical fiber, an optical fiber base material is drawn while being heated by a furnace. The drawn optical fiber then is passed through a cooling device in order to reduce the temperature of the fiber before it is coated with a protective resin. However, the draw speed of the optical fiber is limited by the rate of cooling of the optical fiber. That is, as the draw speed of the optical fiber increases, the cooling capacity of the cooling device must also be increased since the temperature of the optical fiber is increased.
Conventional cooling devices typically include a housing having an inner chamber containing a gaseous medium (e.g., air or helium) which is utilized to cool an optical fiber as it transported through the chamber. Further, the housing may include pipes through which a liquid refrigerant flows. The pipes are used to cool the gaseous medium which fills the inner chamber of the cooling tube in order to remove heat from the optical fiber. However, conventional cooling devices typically require a large amount of heat transfer fluid and are very long thereby requiring a large amount of space on a draw tower. Further, the opening or hole in the conventional cooling devices through which the optical fiber passes is so small that vibrations in the fiber may cause the fiber to touch the sides of the heat transfer apparatuses.
U.S. Pat. No. 5,568,728 discloses a filament cooler including an axial through hole which passes through a plurality of successive inner hemispherical wells or chambers. As shown in FIG. 4, copper pipes 14∫17 are provided for carrying cooling water which reduces the temperature of four strips 18-20 of aluminum which are bolted together around copper pipes to form housing body of the filament cooler. That is, the copper pipes 14-17 are disposed outside of hemispherical wells 29 so that the walls of the hemispherical wells 29 are chilled rather than the helium gas directly. Helium gas is tangentially injected into and extracted from the spherical chambers to induce a cyclonic or swirling gas flow. However, the turbulent gas flow can cause the optical fiber to vibrate or become laterally displaced so that the optical fiber may contact the walls of the of the axial through hole through which the optical fiber passes thereby damaging the optical fiber.
In view of the disadvantages of conventional cooling devices, it is an object of the present invention to provide an optical fiber cooling apparatus having a large heat transfer surface with reduced heat transfer fluid consumption.
It is yet another object of the present invention to provide an optical fiber cooling apparatus having a reduced risk of the optical fiber being damage by contacting the inner walls of the cooling apparatus.
It is a further object of the present invention to provide an optical fiber cooling apparatus having a shorter length in order to save space on the draw tower and enable high draw speeds.
The present invention is adapted to achieve the foregoing objects. In accomplishing these objects, the present invention provides an optical fiber cooling device comprising a plurality of inner chambers through which an optical fiber is sequentially transported.
According to the present invention, there is provided a cooling device comprising a housing body having a plurality of inner cooling chambers which are partitioned from each other by a plurality of partition walls. An axial through hole extends through each of the inner cooling chambers from an upper end of the housing body to a lower end of the housing body for the axial passage of an optical fiber therethough. A plurality of gas injection holes corresponding to the inner cooling chambers are provided in a side wall of the housing body for injecting gas into the inner cooling chambers. A plurality of coolant pipes through which a liquid coolant is circulated extend through each of the inner cooling chambers from the upper end to the lower end of the housing body. The coolant pipes are disposed between the gas injection holes and the axial through hole so that the gas which is injected into the inner cooling chambers via the gas injection holes is not blown directly against the fiber. In other words, the coolant pipes disrupt the flow of the gas as it is injected into the inner cooling chambers thereby preventing the gas blowing directly on the optical fiber. As a result, vibration of the optical fiber is preventing thereby allowing a smaller through hole to be utilized.
The above and other features of the invention including various and novel details of construction and process steps will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular apparatus and method for cooling an optical fiber embodying the invention is shown by way of illustration only and not as a limitation of the invention. The principles and features of this invention may be employed in varied and numerous embodiments without departing from the scope of the invention.